Induction heating apparatus



July 14, 1931. o. NElss 1,814,225

INDUCTION HEATING APPARATUS Filed nec. 5. 192s Patented July 14, 1931 UNITED STATES PATENT OFFICE OSKAR NEISS, F HAMBURG, GERMANY, ASSIGNOB OF lONE-HALF T0 HERMANN BOLLMANN, 0F HAMBURG, GERMANY INDUCTION HEATING APPARATUS Application tiled December 5, 1928, Serial No. 823,810, and in Germany December 7, 1927.

or passages serving to accommodate the medium to be heated. Such an arrangement may consist of the short circuited armature of an asynchronous motor which is prevented from rotating and is provided with a m short circuited winding made up of tubular elements through which the medium to be heated is led. In devices of this kind the power or heating effect has been controlled by varying the leakage between the primary Winding and the short circuited winding or that at some other part of the magnetic circuit. To make this possible the body containing the heating elements had to be capable of variation of position relatively to the 2G rotary field, this necessitating the separation of the primary and secondary parts of the apparatus and resulting in an increase of the resistance of the magnetic circuit. Furthermore due to the mechanical stress caused by the magnetic pull acting upon the heating body, such arrangements have proved useless or defective in practice, their electrical efficiency and power factor being low.

The present invention relates to a heating c arrangement employing a rotary magnetic field, wherein the defects referred to are eliminated without the requisite adjustability or regulation of the heating effect being impaired. To this end according to the invention the tube or conduit system constituting the secondary winding is embedded in a conrmon closed magnetic circuit with the primary winding. It is also possible to utilize a plurality of rotary fields in conjunction with a single tube system and to regulate the power by adjustment of the phase difference or differences of said fields. Other features of the invention will appear hereinafter. 1

One embodiment of the invention is il1ustrated by way of example in the accompanying drawings in which:

Fig. 1 is a perspective view of the device as constructed to employ two rotary fie1ds.

Fig. 2 is a horizontal transverse section thereof.

Fig. 3 is a diagram of the rotary fields.

In the drawings the reference numeral 1 indicates a laminated iron body or core for carrying the magnetic flux, 2 an exciting primary winding connected to the mains, 3 va secondary multi-phase short circuited tube system and 4 la heat insulating medium.

The tube system 3 behaves'like the Winding of the short circuited rotor of an excited multi-phase motor which is stationary. To eliminate mechanical stresses acting upon the secondary system, factors which would be re garded as being disadvantageous in this respect in the case of a motor are enhanced according to this invention by accommodating the secondary winding 8, serving as a heating winding, in a common iron body l togather with the primary winding 2. Thus the invention provides for the complete closure of the magnetic circuit, eliminating any air path and thereby avoiding magnetic or mechanical stresses.

If the best or maximum heating effect is to be obtained in the heating winding it is important that said heating winding be arranged in a certain manner in the iron core and in relation to the primary winding, that is how the rotary field intersects the heating Winding. The number of slots for the primary winding should be divisible by the number of slots for the secondary winding to give a whole number, i. e., should have a common factor therewith, so that considering either the primary or the secondary winding two slots of the windings are always opposite to each other. In the preferred case thenumber of slots for the two windings should be equal. Since according to this invention they are accommodated in a common iron body like orv contiguous portions of the two windings may be arranged to lie in opposite end portions or branches of one and the same slots. By this arrangement it is possible to eliminate almost completely all bending stresses actg upon the heating tubes.

According to a further feature of the invention the length of the tubular elements of the heating winding 3 is not limited to the length acted upon by the magnetic field; on

the contrary the tubular elements may be lengthened beyond the extent of the active magnetic iron of the body 1,1. In other words, the radiating surface of the heating winding traversed by the current may be increased not only by increasing the number of the tubular elements but also by lengthening the same. The use of this arrangement in the known devices would render illuwry their regulability by adjustment of the heating winding relatively to the rotary field. This feature of the invention has the advantage that the so-called short circuit current strength may thereby be brought in a simple manner t0 'the value appropriate for the power of the primary winding without it being necessary to employ means, whether of an ohmic or inductive character, which are not free from losses.

, In heating systems which are very long in relation to the length of the induced portion thereof, it is posslble to cause several such rotary magnetic fields to act upon a common secondary system before the individual tubular elements of the heating system are short circuited together. The heating device may thus be extended to any`desired length and in the case of a medium to be heated flowing through the heating winding the device may lfor FJsimpl heatingwinding and selectin the material gree of the phase displacement.

be divided, say, into initial, intermediate and final heaters; alternatively where no increase of the initialpotential is desired over the entire length of the heating winding provision may. be` made of auxiliar heaters which merely have to cover the ra iation losses. In

this manner it is simply possible to combine individual devices to form-groupsor units or to attain an increase in output or power without enlarging 'the heating system.

Regulation-of the outputmay be provided by suitably dimensioning the therefor, if itis not preferre to eii'ect this -by other 'means such as variation of the leakage, of the number of ampere turns on the primary winding or of the ohmic resistancex as in known arrangements. Regulation 'nlay also be effected on .the following principle. If'two separate rotary, magnetic fields act upon a common heating system, then the. total power transferred to the heating syem is a function of the geometrical sums of the two rotary fields so acting. If the sum is zero, that is if there is a phase displacement of 180 electrical de ees between the fields, then the power trans erred will also -be zero and no heat will be evolved. Thus the heatin effect of the heating winding ma be infinit regulated or varied in depen ency upon t e de- Thisregulation by control of the phase displacement of several rotary fields rela` tively to one another has the advantage over known arrangements that` there is no necessity for mechanical displacement of the. heatrelatively to the primary wind-i netie resistance and thus a reduction of t e power factor would not be caused, since the relative osition of the heating body to the rotary eld is invariably the same. The phase displacement may be controlled automatically by a heat sensitive regulating de:

vice and may be effected by varying the velocity of the rotary field.

In .the specifi construction disclosed showing the invention embodied in a device having two rotary fields, 1 and l, respectively, designate the laminated cores or piles of sheet metal of the u per and lower fields, the core 1 being provided with. the primary exciting winding 2, arranged in group divisions 2', 2", 2"', 2', 2"', 2' in slots therein about the tube system 3 e tending through both cores and serving as Itghe secondary winding, the tubes 3 being united at their ends by rings or heads 5 which inay or may not serve as intake and return or discharge headers. The lower core 1 is provided with a rimary winding 6 ara/nged in.group divisions 6', 6", 6"', 6', 6",

. Fig. 3. illustrates a diagram in which 2 and 6 represent the notary fields, 7 represents the zero point, 7, 9 the potential circle, and 7, 8 is the vector sum representing the magnitude of the net effect o and'. t

The dotted lines and arrows show how the ields a and e are displaced in both piles. 2' 2", 2', 2', 2, 2"' as shown illustrate the successionof the dis laced phases in the up- `per rotary field a (Flg'. l), and 6', 6", 6"', 6', 6", 6"' the succession of .the displaced phases in the lower rotary eld e.

The results produced by the alternating current are as follows.: Y,

To pbtain the maximim heating effect the phases must bedparallel in both of the laminated cores, an the' alternating current has .to move the same/way.

The heating effect is equal to naught in case the two rotating'felds-2 the phases are parallel in both of the lami-; i

nated cores 'and the alternating current movesl,

the oppositefwayfI Y The order of succession of the phases shown, i. e.; 60 in opposite directions, ro-vl duces 66%% of the maximum heating e ect. To obtain the maximum heating effect of 100% the succession of the phases in rotary l field e has to be changed as follows: 6', 6',

6", 6', 6"',e 6": The latter heating effect corresponds to diameter 7, 9 of the power circle shown in the diagram. To reduce the heating effect to 331,% it is -necessary to change the succession of the phases in the lower rotary field e as follows: 6', 6, 6, 6', 6l,a

Apart from the multifarious possibilities of use or applications of such a heating arrangement in the chemical industry for suoli purposes as'producing or dissipating mists and cloud, gasification and heating, it represents an important advance in the steam rais- 10 ing art generally, being applicable `with economical results to the production of dry steam and to the bridging of the distance separating producer and consumer and also in particular to the production of high pressure steam.

I claim l. An induction heating apparatus of the type set forth comprising a plurality of pri* mary windings and a tube or conduit system 20 for containing the medium to be heated and constituting a secondary winding, each primary winding being embedded with the secondary winding in a common closed core, and the secondary winding being prolonged beyond each core, said primary windings presenting a plurality of independent rotary fields in phase displacement to regulate the heating effect.

2. In induction heating apparatus as claimed in claim l, the disposal of contiguous primary and secondary windings in the same core slot.

8. In induction heating apparatus as claimed in claim 1, the combination -of a plurality of separate magnetic rotary fields with a single secondary tube system.

4. In inducting heating apparatus as claimed in claim l, a plurality of separate rotary fields of varying relative phase ar o rangement between the separate rotary fields for the purpose of controlling the heating effect.

5. An induction heating apparatus employing a plurality of primary windings and 5 multiphase alternating current for the generation of secondary currents in an electric conductor serving as a secondary winding, and arrangedl as a tube system through which the element t0 be heated is conducted, said tube '50 system and each primary winding being embedded in a closed iron magnetic core and prolonged beyond it, and said primary windings presenting a plurality of independent rotary fields arranged so that the phases Within the individual rotary fields are displaced from one another.

In testimony whereof I aiix my signature.

OSKAR NEISS. 

